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diff --git a/ArmPkg/Library/CompilerIntrinsicsLib/Arm/clzsi2.c b/ArmPkg/Library/CompilerIntrinsicsLib/Arm/clzsi2.c
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+/** @file
+  Compiler intrinsic to return the number of leading zeros, ported from LLVM code.
+
+  Copyright (c) 2008-2009, Apple Inc. All rights reserved.
+  
+  All rights reserved. This program and the accompanying materials
+  are licensed and made available under the terms and conditions of the BSD License
+  which accompanies this distribution.  The full text of the license may be found at
+  http://opensource.org/licenses/bsd-license.php
+
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+/**
+  University of Illinois/NCSA
+  Open Source License
+  
+  Copyright (c) 2003-2008 University of Illinois at Urbana-Champaign.
+  All rights reserved.
+  
+  Developed by:
+  
+      LLVM Team
+  
+      University of Illinois at Urbana-Champaign
+  
+      http://llvm.org
+  
+  Permission is hereby granted, free of charge, to any person obtaining a copy of
+  this software and associated documentation files (the "Software"), to deal with
+  the Software without restriction, including without limitation the rights to
+  use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+  of the Software, and to permit persons to whom the Software is furnished to do
+  so, subject to the following conditions:
+  
+      * Redistributions of source code must retain the above copyright notice,
+        this list of conditions and the following disclaimers.
+  
+      * Redistributions in binary form must reproduce the above copyright notice,
+        this list of conditions and the following disclaimers in the
+        documentation and/or other materials provided with the distribution.
+  
+      * Neither the names of the LLVM Team, University of Illinois at
+        Urbana-Champaign, nor the names of its contributors may be used to
+        endorse or promote products derived from this Software without specific
+        prior written permission.
+  
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+  FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+  CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS WITH THE
+  SOFTWARE.
+**/
+
+
+#include "Llvm_int_lib.h"
+
+// Returns: the number of leading 0-bits
+
+// Precondition: a != 0
+
+INT32
+__clzsi2(INT32 a)
+{
+    UINT32 x = (UINT32)a;
+    INT32 t = ((x & 0xFFFF0000) == 0) << 4;  // if (x is small) t = 16 else 0
+    x >>= 16 - t;      // x = [0 - 0xFFFF]
+    UINT32 r = t;       // r = [0, 16]
+    // return r + clz(x)
+    t = ((x & 0xFF00) == 0) << 3;
+    x >>= 8 - t;       // x = [0 - 0xFF]
+    r += t;            // r = [0, 8, 16, 24]
+    // return r + clz(x)
+    t = ((x & 0xF0) == 0) << 2;
+    x >>= 4 - t;       // x = [0 - 0xF]
+    r += t;            // r = [0, 4, 8, 12, 16, 20, 24, 28]
+    // return r + clz(x)
+    t = ((x & 0xC) == 0) << 1;
+    x >>= 2 - t;       // x = [0 - 3]
+    r += t;            // r = [0 - 30] and is even
+    // return r + clz(x)
+//     switch (x)
+//     {
+//     case 0:
+//         return r + 2;
+//     case 1:
+//         return r + 1;
+//     case 2:
+//     case 3:
+//         return r;
+//     }
+    return r + ((2 - x) & -((x & 2) == 0));
+}